This section describes background subject matter related to the disclosed embodiments of the present invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
A glaze is a specialized form of glass and therefore can be described as an amorphous solid. A glass ceramic is a specialized form of a ceramics, which is formed first as a glass and then made to partially crystallize through a designed heat treatment which involves controlled cooling. Unlike traditional sintered ceramics, glass ceramics do not have pores between crystal grains. The spacing between grains is filled with the glass. Glass ceramics share many properties with both glass and traditional crystalline ceramics. After adjusting the composition of glass ceramics by processing technique, the final material may exhibit a number of advanced properties that the traditional ceramics do not have.
Glazes and glass ceramics have been used to provide protective coatings. To form the protective coatings, typically a powder of the ceramic is placed into a suspending medium, to which a binder composition is added, this combination of ingredients produces a slurry which is applied over a substrate which is to be coated, and then the slurry is sintered under controlled time, temperature and environmental conditions. During sintering, when the fluid coating material is cooled rapidly, typically a glaze is produced; when the coating material is cooled slowly, a glass-ceramic may be obtained.
Chamber liners for plasma processing apparatus, and component apparatus present within processing chambers are exposed to extremely corrosive conditions. Such processing apparatus are used in the fabrication of electronic devices and micro-electro-mechanical structures (MEMS), for example and not by way of limitation. The apparatus are frequently constructed from ceramics such as aluminum oxide, aluminum nitride, and yttrium oxide, for example and not by way of limitation. The plasma erosion resistance for these materials in a fluorine containing plasma of the kind typically used for etching silicon-containing electronic device structures is better than a number of materials which were used in the processing art even 5 years ago. However, there is constantly an effort to try to improve the erosion resistance of etch processing components, as a means of extending the lifetime of the processing apparatus. Recently, ceramic materials which provide improved corrosion resistance have been used in place of aluminum oxide or aluminum nitride. Solid yttrium oxide component structures have demonstrated considerable advantages when used as semiconductor apparatus components in reactive plasma processing. The yttrium oxide substrate typically comprises at least 99.9% by volume yttrium oxide, has a density of at least 4.92 g/cm3, and a water absorbency of about 0.02% or less. The average crystalline grain size of the yttrium oxide is within a range of about 10 μm to about 25 μm. One advantageous yttrium oxide-comprising embodiment substrate, developed by co-inventors of the present invention, limits impurities to the following concentrations or less: 90 ppm Al; 10 ppm Ca; 5 ppm Cr; 5 ppm Cu; 10 ppm Fe; 5 ppm K; 5 ppm Mg; 5 ppm Na; 5 ppm Ni; 120 ppm Si; and 5 ppm Ti. A yttrium oxide-comprising substrate of this general composition may also include up to about 10% by volume of aluminum oxide.
In a typical reactive plasma etch rate test, where the reactive etchant plasma contains plasma species generated from a plasma source gas of CF4 and CHF3, a solid yttrium oxide substrate resists etch by the plasma better than solid aluminum oxide substrate or solid aluminum nitride substrate.
No matter which ceramic substrate is chosen for use as a plasma processing component part, the ceramic is not easy to machine into complex shapes. In addition, some advanced plasma-resistant ceramics such as yttria show lower mechanical properties in comparison with high strength ceramics such as aluminum oxide (alumina), aluminum nitride, silicon carbide and silicon nitride, for example. As a result, it is desirable to bond one section of a ceramic component to another section, to provide a desired overall shape, and to combine the advantages of a plasma-resistant surface with a high mechanical strength underlying structure.